Radio apparatus



h. nlu w. N Q SQN mho SSB M-N. mv RWM O\Q TQ .KO .QQWQ Ok.\||\ N n?, I-.. Il l l l l l l I l l l I I I l l I I l l l l l I I l l l I NQN @uw L. m J mw @y .m um x nl 5 l 1 l J /Nlu 7., 5% mnw\ l www. u Thu.. .k n hm MH lm i b h. L wsb E .unix .uxmmkmrmlhw mob ISS .mm v m Qmsum QQ Q N PN Patented Dec. 17, 1935 PATENT OFFICE RADIO APPARATUS John D. Reid, Highland Park, Pal, assignor to Radio Corporation of America, a corporation of Delaware Application November 30, 1932, Serial Nc. 644,951

8 Claimsu (Cl. Z-20) My invention relates to radio apparatus and, a radio receiving system that shall be capable more particularly, to radio receivers adapted to cover a wide frequency range.

In order that broadcast receivers designed to cover the frequency-range between 550 and 1500 kilocycles may be utilized for the reception of signals at higher frequencies, it has been proposed to rst heterodyne the incoming signals down to some frequency within the broadcast range before impressing them upon the receiver. This has previously been accomplished through the use of an auxiliary device popularly known as a converter, which is connected between the antennal and the radio receiver, the latter thus functioning to amplify and rectify the beat frequency.

It is customary to provide the converter with a continuously variable oscillator and with a detector, the tuning of which is also continuously Variable, the several tuningk devices, usually variable condensers, being interconnected for simultaneous operation and a single indicating scale being utilized to indicate the tuning.

In order that a number of short-wave bands may be covered, converters, as a rule, have been provided with a plurality of interchangeable inductors of the plug-in type. Since the same tuning condensers are used, however, virrespective of the particular band it is desired to cover, such converters have a rather serious drawback, namely, the crowding together of the frequency-channels with respect to the dial-scale as the inductance of the coils decreases.

That such is unavoidably the case is apparent from a consideration of the formula indicating I the range that may be covered by a tunable circuit constituted by a fixed inductor and a variable condenser as the latter is varied from its maximum capacity position to the position of minimum capacity, i. e.,

wherein the subscripts 1 and 2 indicate, respectively, the low and high frequency ends of the range. Obviously, as the inductance of the coil is lowered, the range increases, with the result referred to above, namely, the channels become so crowded with respect to the dial calibration that tuning and logging become more and more difficult.

It is, accordingly, an object of my invention to provide a radio receiving system that shall not be open to the objections noted above.

Another object of my invention is to provide of covering widely separated frequency ranges without the use of plug-in coils.

Another object of my invention is to provide a combined long-short wave radio receiver that y shall be more efficient on the several frequency ranges than analogous receivers heretofore known.

The foregoing objects and other objects ancillary thereto, I prefer to accomplish through the use of a broadly tuned frequency-converter, preceding a sharply tunable radioreceiver, rather than through the use of a continuously tunable converter as heretofore. In short, my improved converter system is so designed that, through the use of a plurality of multi-contact switching devices, incoming signals lying in any one of a plurality of short-wave bands may, simule taneously, be heterodyned down to frequencies falling within the C-1500 kilocycle range of the usual broadcast receiver, the adjustment of the receiver proper being relied upon to separate the desired signal from those undesired.

The novel features that I consider characteristie of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specic embodiment when read in connection with the accompanying drawing, in which Fig. 1 is a diagrammatic view of a radio receiving system including a preferred embodiment of my invention, and

Fig, 2 is a rear elevational view of a commercial broadcast receiver modified according to my invention.

Referring to the drawing, a radio receiving system including a preferred embodiment of my invention is constituted by a frequency converter portion I, and a radio receiver portion 3, the latter, preferably, being of the uni-control superheterodyne type. 'Ihe converter portion is constituted by a detector tube 5, and an oscillator tube each tube being provided with input and output circuits whereby incoming radio signals and locally generated oscillations may be combined to form beat frequencies.

The detector tube, in order that maximum sensitivity may be had, is preferably of the screen grid pentode type having an anode 9, a suppresser grid Il, a screen grid I3, a control grid I5, a cathode H, and a heater I9. The oscillator tube may be of the three-electrode type having an anode 2|, a control grid 23, a cathode 25, and a heater 21.

Since, according to my invention, I cause a plurality of incoming signals falling in a. definite frequency band to be simultaneously heterodyned, I provide the detector tube and the oscillator tube not with variable tuned input circuits, but with broadly tuned circuits which may be varied in a step-by-step manner to select the desired frequency band. Specifically, the input circuit of the detector tube is constituted by an inductor 29, one end of which is connected to the control grid of the detector and the other end of which is connected through a conductor 3| to the chassis 32 of the converter portion. The inductor is provided with three intermediate taps from which leads extend, respectively, to switch points designated in the drawing 33, 35, and 31. A plurality of Vcapacitors 3S, having a capacity of at least 5000 mmf. are connected between the cathodes of the'detector and oscillator tubes and the conductor 3|. These capacitors are for the purpose of providing a by-pass for currents at radio frequencies, the presence of which would normally cause a heater supply frequency hum to appear in the output of the system.

A fourth switch point 39 is provided, to which no part of the system is permanently connected,

i and aiiith point 4| from which a connection 43 extends to the control grid of the input inductor. Associated with the switch points is a movable contact member 45, connected to the chassis and the low potential end of the input conductor over the conductor 3|.

An adjustable capacitor 41 is connected in shunt to the entire input inductor and, depending upon with which of the points 33, 35, 31, and 39 the movable contact member 45 isV associated, the input circuit is tuned to approximately the middle of any one of four short-Wave bands. The switch-point 4| directly connected to the grid end of the inductor is utilized to short-circuit the input inductor in the event that it is desired to receive signals, in the broadcast band, directly upon the radio-receiver portion 3 of the system. The manner in which this is accomplished will be more fully explained hereinafter.

It will also be noted from an inspection of the drawing that the cathodes of the oscillator and rst detector tube are connected to the chassis of the converter through a self-biasing resistor 49 shunted by a condenser 5| whereby thecontrol-grids thereof, when the converter is in operation, are maintained at a negative potential with respect to the cathodes thereof.

The oscillator is provided with an input inductor 50 with which are associated a plurality of semi-fixed tuning capacitors 50, 53, 55, and 51, one -terminal of each of the capacitors being connected to the grid end of the inductor, and the other terminals thereof being conductively connected, respectively, to a plurality of switch points 59, 6|, 63, and 65. A feed-back inductor 66, in the anode circuit of the oscillator, is coupled to the input inductor 50.

The low potential end of the oscillator input inductor is connected to the converter chassis over the conductor 3|, as is also a movable member 61 which contacts the switch points.

An additional switch point 69, analogous to the point 4|, is provided whereby the oscillator input inductor may be short-circuited simultaneously with theA detector input circuit.

An inductor 1D, included in the screen-grid circuit of the detector tube, is inductively coupled to the oscillator input and output inductors, whereby locally generated oscillations may be impressed upon the detector.

An antenna inductor 1| is coupled to the detector tube input inductor, one end of the coil terminating in a binding post 13 or a flexible lead adapted to be connected to an antenna, and the other` end being connected to an elongated switch point 15, or to a plurality of inter-connected points, (not shown) corresponding in arc to the first four positions of the switching devices associated, respectively, with the detector tube and the oscillator tube.

An additional unconnected switch point 11 is also provided. With the points 15 and 11 is associated a movable contact member 19 connected to the converter chassis o-ver the conductor 3|.

The several switches are connected together for simultaneous actuation as indicated by a dotted line 8| on the drawing.

The converter is supplied with screen grid, anode, and heater potentials from the potential supply system in the radio receiver proper.

The radio receiver which I have chosen to exemplify my invention is of the uni-control superheterodyne type having a radio frequency amplier tube 83, an oscillator tube 85, a iirst detector tube 01, an intermediate frequency amplifier tube 89, a second detector tube 9|, and an output or power amplifier tube 93. Since receivers of this general type are now well known to those skilled in the art, no necessity is seen for illustrating the various circuit connections whereby the radio and intermediate frequencies are transferred from tube to tube and the several tubes are supplied with cathode, anode, and grid biasing potentials. Also, the receiver need not necessarily be of the uni-control type, though this is desirable, since the specic manner in which the radio frequency circuits and the oscillator circuit of the standard wave receiver are tuned forms no part of my present invention. It is fairly important, however, that the input or antenna coil of the receiver have a natural frequency below the low end of the range from which the receiver tunes, for best results.

In the specific receiver illustrated, the output tube 93 is of the screen grid pentode type having a cathode-heater supplied from a secondary winding 91 on the main power transformer in the receiver and being supplied with screen grid potential from the receiver rectifier, (not shoum), over a conductor 99.

In order that the converter portion of my improved receiver may be provided with screen grid, anode and heater potentials, I interpose an adaptor plug mi between the prongs of the output tube 93 and its socket, (not shown), the several potentials then being available to the converter over conductors |03, |05, and |01, respectively, which extend from the adaptor.

The screen grid of the detector tube and the anode lof the oscillator tube are supplied withl It will also be noted that, wheny the movable contact member 19 associated with the detector input circuit is in any one of the rst four positions, an inductor `||5 and a condenser H1 are effectively connected in shunt to the input inductor of the receiver, as indicated in dotted lines. The-inductor is of Such size that, when so connected in shunt to the input inductor, the two inductors in parallel have a natural resonant period lying approximately in the middle of the range vof beat frequencies which the converter is intended to develop.

During the recep-tion of short waves, the converter functions to simultaneously heterodyne a plurality of incoming signals, depending upon the position of the movable switch arms, and a plurality of beat frequencies are simultaneously impressed upon -thereceiverportion. The constants of the system are so chosen that, irrespective of the band being covered, the-beat fre quencies produced fall withinthe tuning range of the receiver and the separation of the desired signal from those undesired is accomplished through adjustment of the tuned circuits in the receiver. The radio receiver portion, therefore, may be tuned, as usual, and, although the input signal thereto is not the original short Wave itself, but a beat frequency produced therefrom, the receiver-dial markings, if calibrated in 10 kc. divisions, still represent 10 kilocycle separation.

Referring torFig. 2 of the drawing, which is a back view of a commercial radio receiver modied according to my invention, I find it eX- pedient to mount the converter unit I upon the inner surface of one of the side walls ||9 of the cabinet. All of the apparatus constituting the converter, with the exception ofthe detector and oscillator tubes, is enclosed within a shielding container |2| and I also nnd it-preferable to enclose the tubes in individual shields |23 and |25 for the purpose of minimizing pickup from local broadcasting stations during short-wave reception. The shielding container constitutes the chassis 32 of the converter portion referred to above.A

The several switches in the converter unit are ganged together, and an actuating shaft |2'|,'

carrying a knob |29, and an indicating pointer 3|, extends through the cabinet wall in order that the said converter may be adjusted for the different frequency ranges. Although not shown in the drawing, an appropriately inscribed escutcheon plate surrounds the switch actuating knob |29 to indicate which of the tuning ranges the receiver is adjusted to cover.

In a preferred embodiment of my invention, the band Waves covered by the converter when the switch is in the first four positions are respectively 15,340 to 15,000 kc.; 11,900 to 11,700 kc.; 9,600 to 9,500 kc.; and 6,150 to 6,000 kc. In each case, the band width in kilocycles is not greater than 250 kc., which range is easily handled by the usual radio receiver that is designed to cover the standard broadcast range of 1,500 to 550 kc.

Since all tuning adjustments are effected from the switch and the tuning of the radio receiver portion, it will be appreciated that considerable interference with short-wave reception may be caused by nearby powerful long wave broadcasting stations. Such interference may be eliminated in each range by shifting the oscillator frequency, resulting in an equal shift in receiver dial setting. This result is accomplished by adjusting the semi-fixed condensers associated with the oscillator to values best suited to local conditions.

It is also highly desirable that all leads between the converter portion and the radio receiver portion be effectively shielded and that the 5.;

shielding braid be grounded into the receiver chassis.

Under certain conditions, where local interference from long Wave broadcasting stations is particularly diiiicult to obviate, I find it desirable 10 to utilize a short antenna, of from 15 `to 30 feet in length, for short wave reception. I also have attained excellent results by including a wave trap |32 in the connection to the short-Wave antenna, as shown in dotted lines in the drawing. 15...

This trap may be so constructed as. to attenuate the entire broadcast band, or it may be specilically designed to reject the most troublesome lnterfering stations.

Since the short antenna, when connected as 20' described, will not operate satisfactorily for long wave reception, an additional antenna connection |33 to the switch point 'l5 is provided. This antenna serves as additional ground area during short wave reception, and, if desired, it may be 25 erected to function as a counterpoise.

Furthermore, the receiver itself, preferably, should not include any exposed coils which function at radio frequency and it is very desirable that no unshielded leads be outside of the chassis 30 shield.

It will be apparent from the foregoing description of my improved receiver that its principal advantage lies in the uniformly greater separation of short-wave stations on the tuning dial that 35 is obtainable. An outstanding feature, also, is that the same dial in the radio receiver portion is used for tuning both the-,short and long wave bands and the dial divisions always represent 10 kc. This gives excellent separation of the short 40 wave stations, and greatly increases the ease with which they may be tuned in and logged.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are pos- 5 sible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention: 50

1. In a radio receiver, a broadly tuned frequency converter portion, a relatively sharply tunable beat-frequency amplifier portion, switching and circuit means for effecting a connection for an energy collector to either portion, at will, 55 and means simultaneously operable with said switch means for altering the input circuit constants of said amplifier portion, and said rst named means including a permanent connection between the amplifier portion and the connection 60 for said energy collector.

2. In a radio receiver, a broadly tuned frequency converter portion, a relatively sharply tunable beat-frequency amplifier portion, a plurality of antennae, switching and circuit means 65 for at will connecting one of said antennae to the frequency converter portion and grounding the other antenna or removing the ground connection from the last-mentioned antenna and effectively coupling it to the input circuit of the beat fre- 70 quency amplier portion, and means providing a connection for the frequency converter portion with the input circuit of said beat frequency amplifier portion.

3. In a signal receiving system, a receiver 75 i verter coupled jointly to said inductor, means for decoupling said antenna circuit, selector means for tuning said frequency converter to provide a plurality of beat frequency signals, means for tuning said input circuit to a predetermined frequency, and means for rendering said frequency converter inoperative to produce beat frequency signals. v Y

4. The combination with a tunable radio receiver having a signal input circuit, of a broadly `tuned frequency converter comprising an electric discharge oscillator tunable selectively to each one of a plurality of different signal frequencies, a switch for effecting said selective tuning, a detector coupled to said oscillator., said detector having an output anode circuit connected with said receiver input circuit, a tuning inductor for said input circuit, an antenna circuit coupled to said detector through said anode circuit connection, means for selectively tuning said detector to each one of a plurality of 4signals at differing frequencies, said selecting means including a switch, selector means for connecting said antenna circuit to ground and said tuning inductor across said input circuit, said last-named means including Ya selector switch, and means for simultaneously operating said switches.

5. In a radio receiving system, an oscillator circuit comprising an inductor, a plurality of semifixed tuning condensers therefor and a selector switch for selectively connecting each of said condensers with said inductor to tune it, a detector comprising an electric discharge device having a signal input grid and an electrode other than said grid coupled to said oscillator inductor, an input circuit for said detector comprising a second inductor and selector means for tuning said inductor to a plurality of different signal frequencies, an antenna circuit coupled to said last-named inductor, means forr grounding said antenna circuit through said coupling means, an output anode circuit, for said detector connected with the receiver input circuit, means providing a signal conveying connectionbetween the antenna circuit and said receivervinput circuit through said output anode circuit connection, and a tuning inductor for said input circuitV in said last-named connection.

6. In a radio receiver, a broadly tuned fre- 5 quency convertor portion, a relatively sharply tunable 'beat-frequency amplifier portion, and switching and circuit means for effecting a connection for an energy collector to either means,

said last named means including a coupling windy ing means including contacts for grounding said M last named end of the coupling winding when operating in a predetermined higher frequency range.

'7. In a radio receiving Ysystem including a tunable signal receiving portion anda frequency cony vertor portion, the combination of a frequency convertor tube in said last named portion having an output anode circuit coupled to said tunable signal receiving portion-an antenna circuit coupled tol the input electrode of said frequency convertortube and including a coupling winding, one end of which is connected to the anode circuit through a series condenser and high frequency choke coil, and switching meansv for selectively connecting said end of the coupling winding to ground.

8. The combination with a radio receiver having a signal input coupling inductor, of frequency converter means including an electric discharge detector device having an output anode, a control grid and a second grid between said control grid and the output anode, a signal input circuit connected withsaid control grid,v an oscillator connected with said second grid, an anode cir'- cuit including said input inductance connected with said anode, an antenna circuit including a coupling inductance and a high frequency choke coil in series with said input inductance through connection with said anode circuit, and switching means for grounding the connection between said antenna inductance and said high frequency choke coil.

JOHN D. REID. 

